How would I know if it is an internal bypass?
If the engine is an external bypass, the thermostat housing connects to the water pump with a short bit of hose, similar to this:
If the engine is an internal bypass, which the later models are (not sure what year they switched) then this connection is in the block and head. There is an extra hole in the front end of the block, between the front passenger side head bolt and the middle head bolt, where coolant can flow into the head/thermostat from the block.
Here's a picture of my old external bypass head, and circled is the spot where the internal bypass hole is located. The head gasket that was under this head was a late model head gasket, and had the hole in it for the bypass. The internal bypass heads have a bump on the end of the head and a hole that corresponds the mark left by the old gasket on my head.
Pete
